WASHINGTON, Jan 15 (Reuters) - President Barack Obama sought to build a united front with Democratic senators on Wednesday, inviting them to the White House to chat about "shared goals" heading into midterm elections in which Republicans will try to exploit Obama's woes to pick up seats.

Obama urged senators to hold off on a proposed Iran sanctions bill that many support - and which he has vowed to veto. The White House has said the legislation would derail an international deal to curb Iran's nuclear program.

But the discussion on sanctions was a small part of a meeting with a decidedly upbeat tone, a Senate aide said, speaking on background.

Obama, not known for his tendency to schmooze, sat on a stool with a microphone in the ornate East Room of the White House, giving brief remarks before taking questions from senators for about 90 minutes.

"The group discussed their shared goals for 2014, and the president expressed his desire to continue to work together to advance a number of our priorities for the year to strengthen our economy, create jobs and build the middle class," the White House said in a brief statement about the closed-door session.

The meeting comes as Obama's favorability ratings continue to languish after the botched launch of his signature Obamacare healthcare reforms last year.

Criticism of the rough start has ebbed after the White House led frantic efforts to fix the website used to sign up for health insurance. But the fallout from that and continuing attacks by Republicans on the Affordable Care Act has made Democrats nervous about the midterm elections.

A group of 16 Senate Democrats will be defending their seats in November, and Republicans are aiming to gain six seats to try to take control of the 100-seat chamber.

At a Republican briefing on Tuesday, officials told reporters they are intent on centering their campaign around Obama's weak approval numbers and the problems with Obamacare - factors they are confident will help them gain seats.

Conservative activists have backed a $2.5 million television ad campaign against three Democratic senators over Obamacare, including North Carolina Senator Kay Hagan.

Republicans have also sought to highlight examples of divisions between Obama and Democratic lawmakers. For example, they publicized that Hagan chose to stay in Washington on Wednesday instead of traveling to her home state of North Carolina with Obama, who was there to talk about manufacturing.

Obama has had trouble working with Congress, but has beefed up his White House staff with people known for expertise in nurturing strong relationships on Capitol Hill.

He wants to press Congress to boost the minimum wage - a mission that polls well, casting Democrats in a favorable light relative to Republicans, who are likely to kill the measure because they control the House of Representatives.

But Obama and his top aides have acknowledged that they are unlikely to get major legislation through the divided Congress.

Obama has brought in John Podesta, a chief of staff to former President Bill Clinton, to help the White House advance actions he can take without Congressional approval.

Those plans will be highlighted in Obama's State of the Union address on Jan. 28.